Jinns are real and in English terms they're called "shadow people" or plasma beings.
Iblis is a jinn, and the bad jinns are shaytans.
There's a Surah al-Jinn in the Quran, Surah #72, and many ayahs speaking of jinns, like from Surah al-Hijr 15:27=
"And the jinn We created before from scorching fire."
The idea of jinns possessing our bodies is problematic. There's no ayah or sahih hadith that tells us jinns can do it.
Most, incidences of possession were cases of mentally unstable person. People confused it with jinn possession.
However, jinns can harm us without possessing a human. They can throw things, strike fear and even make us see things that aren't there. But can they take over our body? No ayah or hadith says they can. But no ayah or hadith says they can't either.
Scholars debated the actuality of possession for over a thousand years.